The reduction of line dimensions in integrated circuits and the increase in the electronic device speeds has led to the need for high-speed probes with sub-micron spatial resolution. The new generation of high-speed electronic devices are designed with sub-micron features in transverse dimensions as well as depth.
Conventional means of visualizing such dimensions include the scanning electron microscope and a class of scanning probe microscopes. Electron-beam testers are the only tool used to measure the internal workings of circuits with nanometer resolution. These systems are highly specialized and require measurement in high vacuum. Electron interaction with the surface of devices also leads to damage. Finally, the bandwidth of these test systems does not exceed 20 GHz. Another of the conventional means of testing such high-speed electronic devices is a network analyzer. This does not have a capability to see the internal node of the device under test. Such network analyzers only measure the relationship between the input and output of the device and assumes the internal working of the device.
Others have done experiments which utilize the high-speed, nonlinear properties of the tunneling current in a scanning tunneling microscope to achieve picosecond temporal resolution. This is not practical as a test method because the feedback mechanism which controls the probe tip's position uses the parameter which is to be measured. Tunneling current is also highly nonlinear.
One other group is using atomic force techniques, but their probe again uses the same mechanism to sense electrical signals as that used in forming an image of the circuit.
A second class of probes are electro-optic and photoconductive probes. Both of these measurement techniques were developed in systems which are integrated with the device under test. Both have also evolved into external probes. Neither has the ability to resolve signals on sub-micron features. Aside from the fact that they do not have means of visualizing the circuit under test, the optical probe is not capable of resolution finer than a single micron and the bulk photoconductive probe is likely to damage the circuit or to be damaged itself due to lack of flexibility.
In general, the prior art electronic testers can be grouped as follows:
e-beam voltage contrast
50-ps temporal resolution PA1 high vacuum required electro-optic probe PA1 1-.mu.m spatial resolution PA1 no internal node testing PA1 10-ps temporal resolution. PA1 feedback control independent from signal; PA1 the use of photolithography which lends itself to mass production; (see Section 2 of Reference 7 noted above and, in particular, pages 5248-5250). PA1 low-force contact with active feedback insures both sensitivity and absence of damage to the device under test. PA1 probes use identical mechanism (i.e. the probe uses the same physical mechanism for imaging feedback and electrical waveform acquisition or two separate probes) for feedback and signal acquisition or two separate probes; PA1 fabrication does not lend itself to mass production; PA1 contact or lack thereof limits the probes ability to make sensitive noninvasive measurements.
electro-optic probe
network analyzers
Relevant publications include:
1. Koichiro Takeuchi and Yukio Kasahara, "High-Speed Optical Sampling Measurement Of Electrical Waveform Using a Scanning Tunneling Microscope", APPL. PHYS. LETT. 63 (26), 27 December 1993 (Received 27 Jul. 1993). Teratec Corp. 2-9-32 Naka-cho, Musashino, Tokyo 180 Japan.
2. S. Weiss, D. F. Ogletree, M. Salmeron and D. S. Chemla, "Ultrafast Scanning Probe Microscopy", APPL. PHYS. LETT. 63 (18), 1 Nov. 1993 (Received 17 Jun. 1993). Lawrence Berkeley Laboratory, Berkeley, Calif. 94720.
3. S. Weiss, D. Botkin, D. S. Chemla, "Ultrafast Scanning Microscopy", OSA PROCEEDINGS ON ULTRAFAST ELECTRONICS AND OPTOELECTRONICS, 1993, Vol. 14, Jagdeep Shah and Umest Mishra (eds.), p. 162. Same address as above.
4. A. S. Hou, F. Ho, D. M. Bloom, "Picosecond Electrical Sampling Using A Scanning Force Microscope", OSA PROCEEDINGS ON ULTRAFAST ELECTRONICS AND OPTOELECTRONICS, 1993, VOl. 14, Jagdeep Shah and Umest Mishra (eds.), p. 166.
5. J. Nees, S. Williamson, J. Kim and S. Gupta, "Picosecond Detector, Optical Temporal Analyzer And Free-Standing Circuit Probe", OSA PROCEEDINGS ON ULTRAFAST ELECTRONICS AND OPTOELECTRONICS, 1993, Vol. 14, Jagdeep Shah and Umest Mishra (eds.), p. 186. University of Michigan, Center for Ultrafast Science, 1006 IST Bldg., 2200 Bonisteel Blvd., Ann Arbor, Mich. 48109-2099.
6. Joungho Kim, Steven Williamson, John Nees, Shin Ichi Wakana and John Whitaker, "Photoconductive Sampling Probe With 2.3 ps Temporal Resolution And 4-.mu.V Sensitivity, APPL. PHYS. LETT. 62 (18), 3 May 1993 (Received 8 Sep. 1992). University of Michigan, Center for Ultrafast Science, 1006 IST Bldg., 2200 Bonisteel Blvd., Ann Arbor, Mich. 48109-2099.
7. C. A. Spindt, I. Brodie, L. Humphery and E. R. Westerberg, "Physical Properties Of Thin-Film Emission Cathodes with Molybdenum Cones", J. OF APPL. PHYS. 47 (12), December 1976 (Received 18 Mar. 1976). Stanford Research Institute, Menlo Park, Calif. 94025.